Disable checkpoint interruption (#236)

* Temporarily disable interrupting of checkpoints.

* Add changeset.

* Skip checkpoint interruption test.

Author: rkistner

.changeset/shaggy-actors-confess.md

@@ -0,0 +1,5 @@
+---
+'@powersync/service-core': patch
+---
+
+Fix hanging sync connections due to checkpoint interruptions.

packages/service-core-tests/src/tests/register-sync-tests.ts

@@ -158,7 +158,8 @@ bucket_definitions:
     expect(lines).toMatchSnapshot();
   });
 
-  test('sync interrupts low-priority buckets on new checkpoints', async () => {
+  // Temporarily skipped - interruption disabled
+  test.skip('sync interrupts low-priority buckets on new checkpoints', async () => {
     await using f = await factory();
 
     const syncRules = await f.updateSyncRules({

packages/service-core/src/sync/sync.ts

@@ -180,7 +180,14 @@ async function* streamResponseInner(
       function markOperationsSent(operations: number) {
         syncedOperations += operations;
         tracker.addOperationsSynced(operations);
-        maybeRaceForNewCheckpoint();
+        // Disable interrupting checkpoints for now.
+        // There is a bug with interrupting checkpoints where:
+        // 1. User is in the middle of syncing a large batch of data (for example initial sync).
+        // 2. A new checkpoint comes in, which interrupts the batch.
+        // 3. However, the new checkpoint does not contain any new data for this connection, so nothing further is synced.
+        // This then causes the client to wait indefinitely for the remaining data or checkpoint_complete message. That is
+        // only resolved when a new checkpoint comes in that does have data for this connection, or the connection is restarted.
+        // maybeRaceForNewCheckpoint();
       }
 
       // This incrementally updates dataBuckets with each individual bucket position.